1. Field of the Invention
The invention relates to energy storage devices and methods for producing energy storage devices.
2. Description of the Related Art
Lithium-ion capacitors are known as energy storage devices. Such lithium-ion capacitors have a combined structure of a negative electrode of a lithium-ion cell and a positive electrode of an electric double-layer capacitor. Japanese Patent Application Publication No. 2011-192888 (JP 2011-192888 A) discloses a lithium-ion capacitor that has: a stack including positive electrodes, negative electrodes, lithium electrodes, and separators; an electrolyte solution; and a laminate outer package. The lithium electrodes are formed into a sheet shape in which lithium foil is crimped onto a lithium-electrode collector made of stainless steel.
JP 2011-192888 A discloses that the laminate outer package containing the stack is injected with the electrolyte solution to be sealed and left for a predetermined time, so that lithium foil dissolves into lithium ions and these lithium ions are pre-doped into the negative electrodes through the electrolyte solution.
In JP 2011-192888 A above, lithium-electrode collectors remain in the interior of the laminate outer package after the pre-doping causes the lithium foil to dissolve. However, the lithium-electrode collectors are unnecessary for the pre-doped energy storage device and it is desirable in terms of cost that unnecessary parts for a finished energy storage device are omitted.